1. Field of the Invention
This invention relates to a centerless grinding method and centerless grinding apparatus. More particularly, the present invention relates to a new form of grinding technology created by combining the through-feed and in-feed schemes that are widely implemented in centerless technology.
2. Description of the Related Art
Centerless grinding is roughly categorized into in-feed grinding and through-feed grinding. Also implemented, to a small extent, are stationary grinding and tangential feed grinding.
FIG. 7 is a front elevation for explaining the fundamentals of centerless grinding.
Work being machined 3 is supported by a blade 1 and a regulating wheel 2 that is a revolving grinding wheel. A grinding wheel 4 that is a revolving grinding wheel makes contact with, and grinds, the work being machined 3 while revolving in the direction of the circular arc arrow R1.
The work being machined 3 is turned in the direction of the circular arc arrow L by the grinding force. The regulating wheel 2 is braked by friction forces while revolving in the direction of the circular arc arrow R2 at a slower circumferential speed than the grinding wheel 4, and controls the speed of revolution of the work being machined 3.
When in-feed grinding is performed, the work being machined 3 is loaded from above in the figure to the position diagrammed and, when the grinding is finished, is unloaded in the upward direction in the figure.
As the outer circumferential surface of the work being machined 3 is subjected to centerless grinding (that being in-feed centerless grinding in this case), the radial dimension of that work being machined 3 will be diminished, whereupon cutting feeding that accords with that dimension is necessary.
However, when cutting, the positional relationship between the regulating wheel 2 and the blade 1 must be held constant, wherefore an upper slide 6 whereon a regulating wheel base 5 and the blade 1 are mounted is fed in the direction of the arrow c in the figure.
As will be understood from FIG. 7, it is also possible to perform cutting feeding by moving a grinding wheel base 8 relative to a base 7 in the direction of the arrow c′.
FIG. 8 is given for explaining through-feed grinding. FIG. 8A is a diagonal view of in-feed grinding for the purpose of comparison, while FIG. 8B is a diagonal view of through-feed grinding.
Fundamentally, in the in-feed grinding diagrammed in FIG. 8A, the upper edge of the blade 1, the centerline a-a′ of the work being machined 3, and the centerline b-b′ of the regulating wheel 2 are mutually parallel.
In the through-feed grinding diagrammed in FIG. 8B, on the other hand, the centerline b-b′ of the regulating wheel 2 is inclined at an angle θ. In FIG. 8B, the drawing of the grinding wheel is omitted, but, more precisely, the shaft of the grinding wheel and the shaft of the regulating wheel are made to incline in a twisted manner, three-dimensionally, by the angle θ, and that angle is called the feed angle.
By the action of the feed angle, a propulsion component is generated against the work being machined 3 in the direction of the arrow a′ (being generated as a component of force in the a axis direction of the friction braking force). For that reason, the work being machined 3 is through-fed in the direction of the angle a′ along the upper edge of the blade 1.
There are advantages and disadvantages in both in-feed grinding and through-feed grinding, respectively. Therefore, in centerless grinding technology, either in-feed or through-feed is selected after considering various work conditions such as the shape of the work being machined and the finishing precision needed.
The through-feed scheme is very convenient because the work being machined is automatically fed. Therewith, although a feed is necessary to compensate for the wear on the grinding wheel caused by long operating hours, no cutting feed is required for finishing the work being machined to the prescribed dimensions.
With the through-feed scheme of grinding, however, it is fundamentally only possible to grind a single cylindrical surface. Technology has been proposed (Japanese Utility Model Publication No. S45-16870/1970), as improved through-feed grinding, wherewith through-feed grinding is performed on a conical surface the apex angle thereof becomes smaller as a cylindrical surface is approached (called a weak conical surface). However, even with this improved through-feed grinding technology, it is only possible to grind a single weak conical surface, and end surfaces, conical surfaces, and step surfaces and the like cannot be ground.
In particular, in through-feed grinding technology, there may be a small-diameter portion that is recessed from the cylindrical surface or a weak conical surface that is the surface being machined, but there may not be any large-diameter portions that protrude from the cylindrical surface or weak conical surface.
In the prior art, the method for machining a β-alumina tube molding disclosed in Japanese Patent Application Laid-Open No. H4-283061/1992 (published) is an example of technology that makes joint use of the in-feed grinding and through-feed grinding described in the foregoing.
With the invention in that prior art, on cylindrical work being machined having portions of different thickness at one end thereof, in-feed grinding is performed in the first half of the process and through-feed grinding is performed in the latter half of the process.
Also, with through-feed grinding, the surface being machined is machined while moving in the axial direction relative to the grinding wheel and regulating wheel, wherefore grinding is done from the leading end of the work being machined. For that reason, the grinding removal amount per single revolution of the work being machined is small, the grinding resistance becomes less, and high-precision machining in a short time is possible.
With in-feed grinding, on the other hand, the entirety of the surface being machined is machined simultaneously, wherefore the grinding removal amount per single revolution of the work being machined is great, and there is a limit to how high efficiency can be raised.
FIG. 9 gives a two-perspective view of five examples of work being machined in centerless grinding.
A simple cylinder as diagrammed in FIG. 9A, or a weak cone having a small apex angle of such degree (a few degrees, for example) that it cannot be easily distinguished visually from a cylinder, is suited to through-feed grinding.
Even when there are portions of small diameter other than the surfaces being machined (indicated by the surface roughness symbols), as diagrammed in FIG. 9B, such work is suited to through-feed grinding.
When there is a portion of large diameter other than the surfaces being machined, as diagrammed in FIG. 9C, through-feed grinding cannot be done.
And, when there is a strong conical surface that is a surface being machined (indicated by the surface roughness symbols), as diagrammed in FIG. 9D, or when the end surface must be machined, as diagrammed in FIG. 9E, such work is not suited to through-feed grinding, even when there is no large-diameter portion.
Thus the cases where through-feed grinding can be applied are rather limited. Work being machined wherewith through-feed grinding is impossible is subjected to in-feed grinding.